In a high-frequency circuit of a mobile terminal such as a mobile telephone, a transmitting circuit and a receiving circuit are selectively connected to a common antenna via a high-frequency switching circuit (a semiconductor switch). A switching element in a high-frequency switching circuit can be a high electron mobility transistor (HEMT) which uses a compound semiconductor; however, because of its low cost and miniaturization, a metal oxide semiconductor field effect transistor (MOSFET) provided on a silicon substrate is widely used instead of the HEMT in such applications.
In a MOSFET type switching element provided on a normal silicon substrate, there is a problem with power loss of the high frequency signal being large since a parasitic capacitance between a source/drain electrode and the silicon substrate is large and the silicon substrate is a semiconductor. Thus, a technology of forming a high-frequency switching circuit on a silicon on insulator (SOI) substrate has been proposed.
In a global system for mobile communications (GSM®), a second harmonic distortion occurring in a high frequency switching circuit when an input power is 35 dBm is required to be −45 dBm or lower in a range from 800 MHz band to 900 MHz band.
In addition, in a mobile terminal which is equipped with a global positioning system (GPS) function and using the 1.5 GHz band, the second harmonic distortion occurring when an input power is 26 dBm is strictly required to be −84 dBm or lower in a range of frequency bands from 698 MHz to 798 MHz.
Further, there is also a maximum allowable input power of the high frequency switching circuit must also be considered.